Two planes were able to fly in and one left Manchester by lunchtime on Friday.

Over the next 24 to 36 hours, prevailing winds will shift slightly to drive the central part of the ash plume further to the north toward Scandinavia, according to BBC weather forecaster Matt Taylor.

"However, later this weekend, they will return to a northwesterly direction and are more likely to bring the risk of ash back to the UK."

Although the winds can be predicted, the crucial factor is how much ash the still-erupting volcano is pumping into the atmosphere.

Hundreds of thousands of people have been stranded in the UK or abroad, many unable to return home as a result of the flight cancellations.

Kerry Stothart, of Maidstone, is stuck in Belgium after being redirected there on their way back from Atlanta.

She said: "We are a party of 10 people including four children, one diabetic, one with ADHD and Aspergers, and a blind lady. This is an absolute nightmare.

"We've had to pay £1,400 for a coach and ferry to take us back home, and that's not until 9pm."

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Scientist Dr Guy Gratton will fly close to the ash cloud in a special plane to analyse the dust

The Norfolkline ferry service between Dover and Dunkirk said it had limited capacity for passengers both on foot and in cars on some crossings.

Experts say the tiny particles of rock, glass and sand contained in the ash cloud could jam aircraft engines, as has happened in previous incidents of planes flying into plumes of volcanic ash.

The Health Protection Agency has stressed the ash does not pose a significant risk to public health, and Health Protection Scotland says only a low concentration of particles is expected to reach the ground.

It advises that some people with respiratory problems may experience short-term effects, but there should be no serious harm.

Nats initially restricted all UK airspace at 1200 BST on Thursday, but allowed some flights into Belfast, Prestwick and Glasgow airports as gaps in the cloud became apparent.

Travel alternatives

It said that a limited number of flights between Northern Ireland and the western isles of Scotland to and from Glasgow and Prestwick would continue until 1900 on Friday, as would North Atlantic traffic to and from Glasgow, Prestwick and Belfast.

Stranded passengers have flooded other modes of travel. Eurostar trains reported a complete sell-out of its services to Brussels and Paris for the second day on Friday.

"We are carrying more than 38,000 people today and all our trains are full," a spokeswoman for the company said.

"We are telling potential customers without bookings not to come to St Pancras because they will not be able to travel."

The Ministry of Defence says 550 military personnel are grounded in Cyprus as a result of the travel restrictions.

Rail and ferry services are reporting rises in their passenger numbers, with ferry operators Stena and Fastnet saying there were significant increases in customers on services departing from Wales.

Extent of Iceland volcano ash cloud

The volcanic eruption in Iceland on Wednesday night sent plumes of ash thousands of feet into the air. The cloud has spread across the UK to Europe.

The spread of the ash cloud at 20-30,000ft raised concerns for air safety, forcing at least 12 countries to restrict or halt flights in their airspace.

The eruptions from the Eyjafjallajoekull volcano continue to pump out ash clouds sporadically, which means the disruption is set to continue.

Although the cloud is too high to pose a health risk, people with breathing problems have been advised to take extra care if it falls to ground level.

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European air traffic control organisation Eurocontrol said some 60% of flights have been grounded and more than half of trans-Atlantic flights cancelled.

Spokesman Brian Flynn added: "Given the fact that this volcanic ash cloud has been quite stable and moving very slowly since it started 48 hours ago, it is reasonable to assume that there will be significant disruption of European air traffic tomorrow."

Northern parts of Germany, France and Poland are also fully restricted

Ryanair cancels all flights to and from northern Europe until 1300 BST on Monday. It will keep running in southern and central Europe, although flight restrictions are being imposed in Hungary and Romania

The Jet2.com airline cancels all its flights on Friday and Saturday, adding additional flights for Sunday and Monday

A small number of flights to and from the west are operating from airports at Dublin and Shannon in the Irish Republic and smaller airports in Sweden and Norway

The Nats extension of restrictions for the UK was the second since Thursday evening.

So far an estimated 600,000 passengers have been affected in the UK.

Transport Secretary Lord Adonis said he was "closely monitoring the situation" and would be meeting key transport officials.

He also said the volcanic ash cloud is expected to cause "significant disruption" to air services for at least the next 48 hours.

Although the Prince of Wales was still due to attend the funeral of the president of Poland Lech Kaczynski on Sunday, his wife, Camilla, the Duchess of Cornwall has had to cancel a visit to a Polish cultural centre in London, Clarence House has said.

The duchess was due to sign a condolence book for the late president but the disruption caused by the ash cloud meant she was unable to travel down from Scotland.

Mr Flynn told the BBC a lack of wind meant the ash cloud was "progressing very slowly eastwards" and remained "very dense".

Ash from the cloud was first detected at ground level on Scotland's Northern Isles on Thursday evening, and early reports from the Shetland islands said that the sky had a light yellow hue on Friday morning.

The Eyjafjallajoekull eruption was the second in Iceland in less than a month.

Volcanologist Thor Thordarsson said if the volcano maintained its current phase of activity, then the eruption could be over in "a few hours or even a few days" meaning the atmosphere would clear shortly afterwards.

But he added: "If the eruption has a phase change and starts to produce lava... then we might be in for a much longer haul, an eruption that might last for months or even years, with a quiet period in between intermittent explosions."

Have you been affected by the volcanic ash cloud? Are you stranded because of the airspace restrictions? Are you in Iceland? You can send your experiences using the form below:

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